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Thread: Buoyancy with a 'breather...

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    Re: Buoyancy with a 'breather...

    Quote Originally Posted by mort
    How do rebreather pilots control their buoyancy?
    Do you do it with loop volume, or do you use a wing bcd that I can't seem to see in pictures, or do you use your dry suit?
    I'm very much a beginner, and I found buoyancy to be pretty depressing during the class. I'm glad I had read about this before hand, so it wasn't a total shock (merely darned shocking instead). Knowing this made it a bit easier to focus on the lessons instead of (uselessly) worrying about looking good.

    Not only was buoyancy an alien ritual (none of my reflexes helped - in fact, they hindered... a lot!), but there are lots of other moving parts to keep up with compared to normal open circuit scuba. My attention got strung pretty thing with task loading.

    Now, each dive is getting a little easier (only 8 post-class dives thus far), and I can see reaching a point some day where I've "re-tuned" my dive reflexes to the rituals that a rebreather needs. My last 3 dives felt like I was actually diving (as opposed to floundering).

    My trim & weighting is dialed in pretty well now, at least compared to my mud-dives during the class.

    I keep loop & drysuit at min volume & tweak my wing as needed. The wing sits between my harness & chasis, pretty much like it would for diving backplate+doubles. I'm slinging a 40cft for bailout now at hip-level, which seems quite comfortable (pleasant surprise, that!).
    My drysuit & lift-bag (100lb) serve as backup buoyancy devices. I don't think I'd like using my drysuit as primary buoyancy device because it would take heat away from me whenever I need to vent gas.

    For a while I'll be practicing/fiddling a lot with buoyancy things - tuning my drysuit's dump valve, fiddling with different dump valves on my wing, and the counterlungs OPV. Just to get a feel for how these things behave at different settings, and learn how to reach them without needing to "think" about where the are and how to use them.


    John G.

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    Re: Buoyancy with a 'breather...

    Quote Originally Posted by fubari
    I'm very much a beginner, and I found buoyancy to be pretty depressing during the class. I'm glad I had read about this before hand, so it wasn't a total shock (merely darned shocking instead). Knowing this made it a bit easier to focus on the lessons instead of (uselessly) worrying about looking good.

    John G.
    I know exactly what you mean. I did all my RB training in a wet suit, to avoid extra taskloading. I'm going out to catalina this weekend, and I'm gonna dive dry. We'll see how it goes, wish me luck.

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    Re: Buoyancy with a 'breather...

    Quote Originally Posted by ROB DAVIE
    The one thing that people who are starting out on rebreathers forget is that changes in "altitude" cannot be made with a simple slight breath, either in or out.
    The more experience that the diver has, the more that this is done on a sub-conscious level. Thus, it is a harder job to retrain one's self.
    And, of course, it is fun to watch....! :D
    I had a very experienced diver in the club pool on mine on tuesday (another poor soul being drawn away by the yellow-side) and he didn't do badly, no banging between the bottom and the surface but he clearly found it frustrating.

    It's mean to laugh but you can get away with it in scuba gear as nobody knows.

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    Re: Buoyancy with a 'breather...

    I think I must have been one of the lucky ones on my rebreather training as I had very little problems with buoyancy on the whole. The only area I found that needed a bit of work was the last 6 metres or so on a blue water ascent - apart from that, I find ascending with the unit easier than on OC.

    I use my drysuit for buoyancy throughout, and I find an automatic dump valve (shoulder mounted) invaluable. I would also advise anybody about to make the transition from OC to CCR (or SCR) to practice buoyancy skills on OC first by using only the BCD or wing and avoiding using exhalation and inhalation for trimming (just breathe in and out as normal throughout). This also has the added benefit of decreasing the potential for venting air through the mask - which should be kept to an absolute minimum on CCR.

    I also found that minor adjustments in depth on CCR can be achieved by using fin strokes (up or down) to maintain the required depth, i.e. if you find yourself ascending, fin downwards first and then adjust suit or wing for buoyancy rather than letting air out first and waiting to drop. As with OC, you will probably find that by finning downwards, the increased ambient pressure will decrease the original buoyancy anyway and you will not need to vent any air - thereby saving gas that would otherwise have been vented and lost.

    I hope the above makes sense. Happy diving.

    PH

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    Re: Buoyancy with a 'breather...

    Maintaining minimum loop volume and using the wing is preferred by most people I know. It takes time and practice and your Instructor will help you out with a lot of advice. The hardest thing I had to stop was that little bit of air I let out of my nose each breath in OC.

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    Re: Buoyancy with a 'breather...

    Quote Originally Posted by mort
    I have been doing a lot of reading online about rebreathers and one question persists in my mind:
    How do rebreather pilots control their buoyancy?
    Do you do it with loop volume, or do you use a wing bcd that I can't seem to see in pictures, or do you use your dry suit?


    (Pardon the questions if this has already been asked.)
    My personal feeling is to only use the drysuit for thermal protection.. keep the gas at a minimum to avoid squeeze.. I keep the ds valve wide open, so it pretty much vents on its own..

    Keep the CL at minimum volume, buoyancy with a wing.. I can maintain neutral throught the water colum without any problems even when task loaded..
    Joe Radomski
    CCR Trimix Instructor Trainer
    ANDI Instructor Trainer Director #10

    All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

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    Re: Buoyancy with a 'breather...

    Quote Originally Posted by JPJones
    ...The hardest thing I had to stop was that little bit of air I let out of my nose each breath in OC.
    One of the tricks to break that habit is to have a bit of water inside your mask covering the nostrels.

    If you breath out thru them, you will know.

  8. #18
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    Re: Buoyancy with a 'breather...

    Answer depends on:
    1. Water temperature.
    2. The type of dry suit.

    Best case is obviously warm water, wet suit then you just have the wing, and fin. Finning to control minor buoyancy issues. Using gas in the loop to control buoyancy is a mistake: keep the loop constant. Easy.

    When people are not looking, I normally dive the worst case: this is an 8mm Unisuit (a Poseidon drysuit made from 8mm neoprene which avoids you freezing to death if your seal tears when you have deco to do), then there is no choice but to use a wing and the suit. The loss of bouyancy from the neoprene compressing from 8mm to 1mm means that from surface to 90ft, I use the suit then from 90ft downwards, use the wing and try and keep the suit constant, as well as the loop. Down very deep, one has to adjust further (90ft the 8mm neoprene is about 3mm, and it keeps compressing). Unisuits are not the most flattering things in the world, especially when pumped up when you are on the surface.

    Otherwise, when I am using an Otter Brittanic, a membrane suit, I use the wing only: I try and keep the gas in the suit just enough to eliminate squeeze.

    Yes, there are three places to think about. Suits are easy to dump, especially if you use neoprene neck seals which have a habit of dumping for you if one forgets (and puts a trickle of cold water in to wake you up!). Wing is the main control, so make sure it does not flap about. Most here use the OMS 110lb lift doubles: if you have a flood on a RB you will need an extra 40 to 60lb of lift. Big wings must be tied down.

    You sound like you might be a cave diver, so I am sure you have all these things nailed down anyway, except possibly a preclivity towards particular aloof suppliers ;). All guesses, so tell us a bit more about what you dive now, and what sort of dives you do.

    Cheers,

    Alex
    Last edited by AD_ward9; 10th December 2005 at 09:22.

  9. #19
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    Re: Buoyancy with a 'breather...

    Pretty diverse answers on this subject. One of the most important things in RB diving is proper weighting, you shouldnt use the CL's for buoyancy, min lung volume is the way to go. I have the inside of my front mounted CL's sewed down to reduce their max volume, helping with that. You should have just enough weight to get you under with an empty BC and not an ounce more. I dive with a drysuit in cold Pacific NW water and keep just enough air to prevent squeeze and keep me warm.
    the issues are as such:
    you dont use much supply gas, expecially compared to OC, like "G" said so not much buoyancy swing there. UNLESS, you have to bail out. If you think about this, you might come to the conclusion that the bailout cylinders will begin to float you as you use them, but, why did you bail out? Flooded loop? the buoyancy that was in your RB is gone, so no problem being too light there. but what if you had a breakthrough, bailed out and there is still gas in the loop, normally it would exchange from being in your chest to being in the CL's, but now the loop has gas and you are inhaling from a bailout cylinder displacing even more water than when you were on the loop. you are going to be too light to maintain a deco or safety stop. Part of your bailout procedure should be to open up your OPV all the way so expanding gas can escape without you having to tend it. You also have the option of delibertly flooding the loop to weight yourself down in an emergency (assuming you are on OC bailout) to maintain stop depth and not blow a deco.

    I find its best to swim up or down for minor corrections to your desired depth, then make adjustments to regain neutral(usually to the drysuit, the ADV, OPV and your breathing will automatically keep the loop at the correct volume, with practice) I avoid using the BC except for floation at the surface.

    Speaking of practice, thats what it takes to get happy with your buoyancy on any RB, lots and lots of practice. we all felt like newbies the first dozen or so dives closed circuit.

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